Retracting-type soot blowers for cleaning the heat exchanging surfaces of large public utility boilers and the like by discharging steam and/or air and/or water against such surfaces in the form of one or more powerful jets are commonly designed to discharge the cleaning jets in a helical or spiral pattern, or, in the case of an oscillating blower, in the form of an alternately reversed incomplete helical or spiral cleaning pattern. In order to index or stagger the jet paths which define the patterns of non-oscillating blowers, it has been known to provide a lost motion connection between the lance tube and its driving hub. Such a lost motion connection, while effective to properly stagger the cleaning path of the jets of continuously rotating, non-oscillatory blowers, is not effective to properly stagger the jet paths of an oscillating blower. If used in an oscillating blower, the known staggering or "indexing" means would introduce an undesirable dwell interval at each reversal of the direction of angular movement during longitudinal travel of the lance. An important object of the present invention is to provide improved means for indexing or staggering the jet paths of oscillatory retracting soot blowers. Another object is to provide such means which is incorporated in a very compact but rugged and reliable mechanism, by means of a simple gear and crank modification adapted to be substituted in place of one of the gears of an accessory transmission conversion unit corresponding to the unit disclosed in said U.S. Pat. No. 4,177,539. Such patented conversion units are designed for selective installation on standard non-oscillating soot blowers, to convert them to oscillating action when desired. The present invention permits such conversion units to selectively function to provide either staggered or non-staggered (indexed or non-indexed) patterns, as operating conditions may require. A related advantage of the invention is that it incorporates readily accessible, conveniently operable means for changing the blowing pattern from staggered to non-staggered form, and vice-versa.
Other objects and advantages will become apparent to persons skilled in the art upon consideration of the present disclosure in its entirety.